The present invention relates to a differential apparatus for vehicles, and in particular, to a joining structure for an output shaft, which outputs torque produced by a driving source, and a differential case.
A differential apparatus for vehicles transmits torque produced by an engine to left and right axle shafts (wheel drive shafts), which respectively transmit the torque to left and right drive wheels. A conventional differential apparatus is disclosed, for example, in Japanese Laid-Open Patent Publication No. 9-229162. The conventional differential apparatus includes a gear case and a ring gear that are integrally formed from the same material. Such an integral structure eliminates the need for assembling the gear case and the ring gear. This improves productivity of the differential apparatus and prevents noise and vibrations, which are produced when the axis of the gear case is misaligned from the axis of the teeth in the ring gear.
FIG. 2 illustrates a differential apparatus 100 that transmits torque produced by a motor to left and right axle shafts. The differential apparatus 100 transmits torque produced by the motor 150, which includes a stator core 152 and a rotor core 154, to a left axle shaft 102 and a right axle shaft 104 while causing a rotational difference between the left axle shaft 102 and the right axle shaft 104. In more detail, the differential apparatus 100 includes a pair of side gears 106, each of which is arranged at one end of either the left axle shaft 102 or the right axle shaft 104. A pair of differential pinions 108 and a pinion shaft 110 are meshed with the pair of side gears 106 to automatically generate a rotational difference. The pinion shaft 110 extends through a gear case 112. With this structure, torque of a motor output shaft 156 is transmitted to the left axle shaft 102 and the right axle shaft 104. The differential apparatus 100 does not need to have a ring gear for transmitting torque from the motor output shaft 156 to the gear case 112. Therefore, the gear case 112 does not have to be assembled with a ring gear, and there are no problems caused by the assembled gear case 112 and ring gear.
One end of the motor output shaft 156 is inserted in the gear case 112 so that internal splines 114 formed around the outer surface of the motor output shaft 156 and external splines 116 formed around the inner surface of the gear case 112 are engaged with one another. This means that the gear case 112, which is joined with the motor output shaft 156 by the internal and external splines 114 and 116, must be positioned at the same time as when the motor output shaft 156 is positioned. Moreover, when the machining accuracy of the internal and external splines 114 and 116 is not sufficient, the axis of the motor output shaft 156 and the axis of the gear case 112 may not be aligned with each other. This may produce noise and vibrations.
Further, the internal splines 114 and the external splines 116 occupy space in the axial direction of the motor 150 (see dimension H). This restricts the maximum size of the mountable motor 150.